Unraveling the Structure of Magic-Size (CdSe)₁₃ Cluster Pairs

Abstract

Cadmium selenide is a II−VI semiconductor model system known for its nanoparticle preparation, growth mechanism, luminescence properties, and quantum confinement studies. For the past 2 decades, various thermodynamically stable "magic-size nanoclusters (MSCs)" of CdSe have been observed, isolated, and theoretically calculated. Nevertheless, none of the proposed structures were experimentally confirmed due to the small crystal domains beyond the diffraction limit. With a combination of nondestructive SAXS, WAXS, XRD, XPS, EXAFS, and MAS NMR techniques, we were able to verify the phase transformation, shape, size dimension, local bonding, and chemical environments of (CdSe) 13 nanoclusters, which are indicative of a paired cluster model. These experimental results are consistent with the size, shape, bond lengths, dipole moment, and charge densities of the proposed "paired-tubular geometry" predicted by computational approaches. In this article, we revisit the formation pathway of the mysterious (CdSe) 13 nanoclusters and propose a paired cluster structure model for better understanding of II−VI semiconductor nanoclusters.

Unraveling the Growth Mechanism of Magic-Sized Semiconductor Nanocrystals

“…This eliminates the possibility that these larger MSNCs have closed-cage or tubular-pair structures, as discussed earlier based on mass spectrometry 16 and XRD experiments. 42 Instead, our results are more consistent with the tetrahedral shape previously proposed. 17,32 This is supported by the isotropic and faceted nature of our particles in electron microscopy.…”

Room‐Temperature Formation Pathway for CdTeSe Alloy Magic‐Size Clusters

“…It is noteworthy that Scheme is consistent with the model proposed for the transformations among the four types of CdTe MSCs, CdTe MSC‐371, MSC‐417, MSC‐448, and dMSC‐371, in that these transformations occur through their own PCs . With relevance to ternary perovskite MSCs, Equation (1) (Steps 1 and 2) provides a deeper understanding for these transformations among the various types of binary ME MSCs . The present findings on the room‐temperature evolution of CdTeSe MSC‐399 with mixed binary CdTe and CdSe induction period samples offer strong evidence support for the two‐pathway model proposed for binary semiconductor quantum dots and MSCs, and contribute to the advance of the nonclassical multistep nucleation models …”

“…The present findings introduce a new approach to synthesizing alloy MSCs at room temperature by mixing binary induction period samples, and they enable further insight into the pathway for the room‐temperature formation of CdTeSe MSC‐399 with and without the complication of CdTe MSC‐371. Also, the present study provides a more complete understanding of the evolution of MSCs and the transformations among them . Similar to the fabrication of small‐size CdS quantum dots with enhanced particle yield from a CdS induction period sample, the room‐temperature synthesis of single‐ensemble CdTeSe MSC‐399 by mixing CdTe and CdSe induction period samples assists in the advance of nonclassical nucleation theory …”

Magic‐Sized Stoichiometric II–VI Nanoclusters

“…Other nondestructive spectroscopic methods such as small angle X‐ray scattering, wide angle X‐ray scattering and PDF analysis are also potential for structure characterization of MSCs. [ 73,76 ] As each one of these analytical methods has their intrinsic limitations, it is highly recommended to verify size and structural results of MSCs using multiple techniques.…”